(a) Field of the Invention
The present invention relates to touch panel devices, and more particularly, to touch panel devices having a conductive layer with a plurality of through holes to vary resistance between the electrodes for specific applications.
(b) Description of the Related Art
Generally, a touch panel is formed by laminating transparent upper and lower conductive layers with a spacer such as a dot spacer interposed therebetween. The touch panel thus formed is mounted on a display surface of a display device such as a CRT or LCD (liquid crystal display), and is depressed at a predetermined position by means of a pen, a finger, etc. as viewed by an operator to detect a coordinate at such a depressed position.
According to a touch panel of a prior art, as shown in FIG. 8, a pair of transparent conductive layers 1 and 3 are disposed to be opposite each other with a certain gap therebetween by a plurality of dot spacers 5. Electrical switching is effected by applying a pen 7, finger or other pressure to a specific location of the layer 1 to make a contact with the layer 3.
When electrically switched on the specific location, a controller 9 detects a voltage which is varied by a resistance of the specific location. The voltage signal is converted into a digital signal by an analog-to-digital converter of the controller 9, resulting in a coordinate position signal. The coordinate position signal is provided to a CPU, which is connected to a display device such as LCD or CRT, to drive the display device.
As shown in FIG. 9, the lower conductive layer 3, which has an active area, is formed on the bottom plate 15. The conductive layer 3 has a pair of electrodes 17 disposed on its edges to be opposed in an X direction. A driving voltage is applied to the electrodes 17. Although the upper conductive layer 1 is not shown in the drawing, it is the same size as the lower conductive layer 3 and is formed on the top plate. The upper conductive layer also has a pair of electrodes disposed on its edges to be opposed in an Y direction.
The resistance R between the electrodes of the conductive layer is determined by a sheet resistance as well as an aspect ratio of the layer, as expressed in the following formula 1:
R=Roxc3x97(x/y)xe2x80x83xe2x80x83[Formula 1]
Where Ro represents a sheet resistance of a conductive layer, expressed in units of xcexa9 or xcexa8/xe2x96xa1, (x/y) represents an aspect ratio of a conductive layer since x and y represent lengths of the conductive layer in X and Y directions, respectively.
The sheet resistance Ro is inherently determined by the material of the layer while the aspect ratio is determined by a design of the layer dimensions. Accordingly, the resistance between the electrodes is also to be determined with respect to a fixed value by the material and design of the conductive layer.
However, there has been needs to have the resistance values of various ranges since various circuit configurations are used for specific applications. In order to adjust the resistance value to meet the needs, additional heat treatment processes are generally used before and/or after the etching process of the conductive layer.
The additional heat treatment processes, however, increase the number of manufacturing processes as well as the processing time. They also require expensive manufacturing facilities.
Further, the heat treatment processes cause excessive uneven distribution of conductive layers, thereby deteriorating manufacturing yields and quality of the touch panel devices.
In view of the prior art described above, it is an object of the present invention to provide a touch panel device of which the conductive layer has various ranges of resistance values as adapted for specific applications.
It is another object of the present invention to provide a touch panel device which is adapted for having a wide-range resistance value without any additional manufacturing process which may produce uneven distribution of a conductive layer.
To achieve these and other objects, as embodied and broadly described herein, the invention comprises
a top plate and a base plate;
a upper conductive layer, formed on the top plate, having a pair of first electrodes disposed on its edges to be opposed in a first direction, the first electrodes being applied by a driving voltage;
a lower conductive layer, formed on the base plate, having a pair of second electrodes disposed on its edges to be opposed in a second direction normal to the first direction, the second electrodes being applied by a driving voltage;
a plurality of dot spacers, located in between said upper conductive layer and lower conductive layer, the upper conductive layer and the lower conductive layer facing each other with a certain specified clearance therebetween; the dot spacers made of an elastic material; and
a controller for detecting a coordinate signal of a position on which the upper conductive layer and the lower conductive layer are contacted with each other by an external pressure,
wherein a plurality of through holes are formed on at least either one of the upper conductive layer and the lower conductive layer, so that a resistance between the electrodes can be varied by varying dimensions of the through holes and intervals between the through holes.
The resistance between the electrodes has a value which is around an ideal resistance determined by the following conditions:
R=Yxc3x97Ro/(nxc3x97W)
n=X/(W+T)
where
Ro represents a sheet resistance of a conductive layer;
X represents a length of each electrode;
Y represents a distance between the electrodes;
T represents a dimension of each through hole; and
W represents an interval between the adjacent through holes.
Both the foregoing general description and the following Detailed Description are exemplary and are intended to provide further explanation of the invention as claimed.